I know this subject has probably been beat to death like Ford and Chevy, but, I am just getting a finder capable of using a map card. I will be getting some type of Humminbird, probably a Helix. What card is best for Texas lakes?

I agree, having both is best. I prefer lakemaster 99% of the time but if I am trying a new lake and looking for things like humps or ponds, sometimes it doesn't have as much detail and switching to navionics, it will. If I had to live with only one then it would be lakemaster.